Current Status of EEG-Based Depth-of-Consciousness Monitoring During General Anesthesia

Monitoring the level of consciousness during general anesthesia with processed electroencephalogram (EEG) monitors has become an almost routine practice in the operating room, despite ambiguous research results regarding its potential benefits. For the patient as well as the anesthesiologist, the primary concern with respect to general anesthesia is that there will be a lack of awareness and recall during surgery. Using EEG signals to monitor the depth of anesthesia should reduce the incidence of intraoperative awareness, lead to a reduction in drug consumption, prevent anesthesia-related adverse events, and enable faster recovery. These benefits have been associated with depth-of-anesthesia monitoring in small clinical trials, but larger studies of EEG-based monitoring have failed to confirm the results of the smaller studies. The results of recent studies that investigated the emergence of consciousness after general anesthesia and the mechanism of action of anesthetic drugs on the central nervous system may help us to understand the limitations of EEG-based monitors and why they do not perform better in large clinical trials. In this article, we review the current status of monitoring the hypnotic component of general anesthesia and discuss the results of recent studies and guidelines that pertain to depth-of-anesthesia monitoring.